This relates generally to wireless communications circuitry, and more particularly, to electronic devices having wireless communications circuitry.
Handheld electronic devices and other portable electronic devices are becoming increasingly popular. Examples of handheld devices include handheld computers, cellular telephones, media players, and hybrid devices that include the functionality of multiple devices of this type. Popular portable electronic devices that are somewhat larger than traditional handheld electronic devices include laptop computers and tablet computers.
Portable electronic devices are often provided with wireless communications capabilities. For example, handheld electronic devices may use cellular telephone communications standards to communicate with cellular networks. Handheld electronic devices typically have small battery with a limited battery capacity that is used for performing wireless communications. Unless care is taken to consume power wisely, an electronic device with a small battery may exhibit unacceptably short battery life.
Electronic devices with wireless communications capabilities typically include amplifying circuits that are used to amplify the power of radio-frequency signals prior to wireless transmission. For example, a radio-frequency power amplifier may receive input signals having an input power level and generate corresponding output signals having an output power level. The radio-frequency power amplifier receives a power supply voltage that powers the radio-frequency amplifier.
The power supply voltage (sometimes referred to as a bias voltage) provided to the radio-frequency power amplifier can be continuously adjusted based on the voltage magnitude of transmit signals that are amplified by the power amplifier in a process sometimes referred to as envelope tracking When performing envelope tracking, the power supply voltage is reduced at times when the transmit signals have a relatively low magnitude (i.e., a relatively low modulation envelope magnitude) and is increased at times when the transmit signals have a relatively high magnitude (i.e., a relatively high modulation envelope magnitude) so that overall power consumption is reduced in the device while transmitting radio-frequency signals. However, if care is not taken, reduced power supply voltages provided to the amplifier while performing envelope tracking operations can be insufficient to ensure satisfactory radio-frequency performance of the power amplifier. When provided with an insufficient power supply voltage, the power amplifier can generate spectral regrowth at harmonics of a transmit frequency that can undesirably interfere with a receive frequency of the device.
It would therefore be desirable to be able to provide wireless communications circuitry with improved power management capabilities.